Mask-programmed read-only memory with reserved space

ABSTRACT

The present invention discloses a mask-ROM with reserved space (mask-ROM RS ). For small content revision, the present invention salvages the original data-mask by writing the data-pattern of new content into a reserved mask-region which originally has no data-pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/396,596, “Mask-Programmable Memory with Reserved Space”,filed Feb. 14, 2012, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/883,172, “Three-Dimensional Mask-ProgrammableMemory with Reserved Space”, filed Sep. 15, 2010, which is acontinuation-in-part of U.S. patent application Ser. No. 11/736,773,“Mask-Programmable Memory with Reserved Space”, filed Apr. 18, 2007,which is a non-provisional application of a U.S. Patent Application Ser.No. 60/884,618, “Mask-Programmable Memory with Reserved Space”, filedJan. 11, 2007.

BACKGROUND

1. Technical Field of the Invention

The present invention relates to the field of integrated circuits, andmore particularly to mask-programmed read-only memory (mask-ROM).

2. Prior Arts

For a mask-programmed read-only memory (mask-ROM), content is writtenusing at least one data-mask during manufacturing process (step 10 ofFIG. 1C). For example, a data-mask 2 comprises a plurality ofmask-regions 2 a-2 i, whose patterns represent content data 4 a-4 i(FIG. 1A). Hereinafter, the pattern representing content data isreferred to as data-pattern. Being permanently formed, the data-patternscannot be modified once written onto the data-mask 2.

In prior art, whenever a new content needs to be included in a mask-ROM,a new data-mask 2 x needs to be made to replace the original data-mask 2(step 12 of FIG. 1C). For example, the new data-mask 2 x includes thedata-pattern of the new content 4 e* in the mask-region 2 e (FIG. 1B),as well as the data-patterns for the original contents 4 a-4 d, 4 f-4 i.The original and new contents 4 a-4 d, 4 e*, 4 f-4 i are written to asecond batch of mask-ROMs using the new data-mask 2 x (step 14 of FIG.1C).

As technology advances, data-mask becomes more and more expensive. Forexample, a 22 nm data-mask costs ˜$260 k. In addition, a data-maskcontains more and more data. For example, a 22 nm data-mask contains upto ˜155 GB data. Some of these data will likely be revised at a futurepoint of time. Replacing a whole data-mask for small data revision iscostly. To overcome this and other drawbacks, the present inventiondiscloses a mask-ROM with reserved space (mask-ROM_(RS)).

OBJECTS AND ADVANTAGES

It is a principle object of the present invention to provide a mask-ROMthat can economically accommodate small content revision.

It is a further object of the present invention to provide a mask-ROMwhich salvages the original data-mask for small content revision.

In accordance with these and other objects of the present invention, amask-ROM with reserved space (mask-ROM_(RS)) is disclosed.

SUMMARY OF THE INVENTION

The present invention discloses a mask-ROM with reserved space(mask-ROM_(RS)). For small content revision, the present inventionsalvages the original data-mask instead of discarding it. On itsoriginal data-mask, at least one mask-region is reserved for a futurenew content and has no data-pattern. Being un-patterned, the reservedmask-region can be used to write the data-pattern of the new content.This differs from prior art. In prior art, because all mask-regions havebeen written, there is no un-patterned mask-region on the data-mask towrite the data-pattern of the new content into.

The mask-ROM_(RS) comprises first and second portions. In its originalversion, the first portion stores an original content, while its secondportion stores no content and forms a reserved space. In its updatedversion, the second portion stores the new content. In the presentinvention, both the updated and the original mask-ROM_(RS) use the samedata-mask (although with revision), not two different data-masks.Because the original data-mask is salvaged instead of being discarded,little extra mask cost is incurred for small content revision. Here,small content revision means the amount of new content that is to beincluded at a future point of time is substantially less than theoriginal contents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B illustrate original and new data-masks in prior art; FIG. 1Cdiscloses a data-writing method to the original and new mask-ROMs inprior art;

FIGS. 2A-2B illustrate exemplary original and updated data-masks 6, 6*;FIG. 2C discloses a preferred data-writing method to the original andupdated mask-ROM_(RS)'s;

FIGS. 3AA-3AB are different views of an original mask-ROM_(RS) array 30;FIGS. 3BA-3BB are different views of an updated mask-ROM_(RS) array 30*;

FIG. 4 is a circuit block diagram of a preferred mask-ROM_(RS);

FIG. 5A discloses an exemplary address-mapping table of an originalmask-ROM_(RS); FIGS. 5B-5C disclose exemplary address-mapping tables oftwo updated mask-ROM_(RS)'s.

It should be noted that all the drawings are schematic and not drawn toscale. Relative dimensions and proportions of parts of the devicestructures in the figures have been shown exaggerated or reduced in sizefor the sake of clarity and convenience in the drawings. The samereference symbols are generally used to refer to corresponding orsimilar features in the different embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Those of ordinary skills in the art will realize that the followingdescription of the present invention is illustrative only and is notintended to be in any way limiting. Other embodiments of the inventionwill readily suggest themselves to such skilled persons from anexamination of the within disclosure.

In this specification, the term “original” refers to the first versionof the mask-ROM, which stores an initial collection of contents, i.e.original contents. The term “updated” refers to the second version ofthe mask-ROM, which stores a large portion of the original contents,plus at least a new content. The new content could be included as anadditional content, which adds to the original contents; or as anupgrade content, which replaces an outdated content in the originalcontents.

In this specification, “content” can be broadly interpreted as astandalone content or a component thereof. Here, “standalone content”refers to information which, by itself, provides value for an end-userin specific context. A content could be a single file or a collection offiles. One example of content is a multimedia content, including atextual content, an audio content, an image content (e.g. a digital map)and/or a video content (e.g. a movie, a TV program, a video game).Another example of content is a computer program, including an operatingsystem, a computer software for computers and/or an application softwarefor cellular phones.

The present invention discloses a mask-ROM with reserved space(mask-ROM_(RS)). For small content revision, the present inventionsalvages the original data-mask instead of discarding it. On itsoriginal data-mask, at least one mask-region is reserved for a futurenew content and has no data-pattern. Being un-patterned, the reservedmask-region can be used to write the data-pattern of the new content.Here, small content revision means the amount of new content that is tobe included at a future point of time is substantially less than theoriginal contents.

Referring now to FIGS. 2A-2C, the original and updated data-masks usedfor a preferred mask-ROM_(RS) and a preferred data-writing method aredisclosed. The original data-mask 6 comprises a plurality ofmask-regions 6 a-6 i (FIG. 2A). Most mask-regions 6 a-6 e, 6 g-6 i havedata-patterns representing data for the original contents 8 a-8 e, 8 g-8i. However, at least one mask-region 6 f is reserved for at least afuture new content and has no data-pattern. This mask-region 6 f isblank, i.e. either all dark or all clear. The original contents 8 a-8 e,8 g-8 i are written into a first batch of mask-ROM_(RS)'s (i.e. originalmask-ROM_(RS)'s) using the original data-mask 6 (step 20 of FIG. 2C).

When a new content 8 f needs to be included in an updated mask-ROM_(RS),the data-pattern representing this new content 8 f is written to thereserved mask-region 6 f (step 22 of FIG. 2C). As a result, the updateddata-mask 6* contains the data-patterns representing the originalcontents 8 a-8 e, 8 g-8 i plus the new content 8 f (FIG. 2B). Thesecontents 8 a-8 e, 8 f, 8 g-8 i are written into a second batch ofmask-ROM_(RS)'s (i.e. updated mask-ROM_(RS)'s) using the updateddata-mask 6* (step 24 of FIG. 2C). In the present invention, the firstand second batches of mask-ROM_(RS)'s use the same data-mask 6 (althoughwith revision), not two different data-masks 2 and 2 x as in prior art.Because the original data-mask 6 is salvaged instead of being discarded,little extra mask cost is incurred for small content revision.

To make it economically feasible to salvage the original data-mask, theoriginal contents should occupy a substantial portion of the originaldata-mask, preferably at least 50% of the original data-mask. On theother hand, when revising the original data-mask 6, it is crucial towrite the data-pattern of the new content into an un-patternedmask-region 6 f. This differs from prior art. In prior art, because allmask-regions have been written, there is no un-patterned mask-region onthe data-mask to write the data-pattern of the new content into.

Referring now to FIGS. 3AA-3BB, an exemplary mask-ROM_(RS) array in itsoriginal and updated versions is disclosed. The mask-ROM_(RS) array 30(or 30*) comprises a plurality of lower address lines (210 a . . . ) andupper address line (230 a . . . ) and mask-ROM cells. Each memory cellfurther comprises at least a data-layer 220, where the existence orabsence of a contact via determines the digital state of the memorycell. Examples of the data-layer include an insulating dielectric or aresistive layer. The data-pattern of the data-layer is defined by thedata-mask 6 (or 6*). For reason of simplicity, diodes, transistors andother memory components are not shown in FIGS. 3AA-3BB.

FIG. 3AA is a cross-sectional view of the original mask-ROM_(RS) array30 along the cut-line AA′ of FIG. 3AB; FIG. 3AB is a top view of thedata-pattern 250 of the data-layer 220 in the original mask-ROM_(RS)array 30 and its relative placement with respect to the address lines210 a . . . ; 230 a . . . . The mask-ROM_(RS) array 30 comprises a firstportion 240A and a second portion 240B. The first portion 240Acorresponds to the region 260A of the data-layer 250, which hasdata-patterns 220 a-220 c. Accordingly, the memory cells in the firstportion 240A are associated with a plurality of data blocks. They storethe original content and form the original data space. On the otherhand, the second portion 240B corresponds to the region 260B of thedata-layer 250, which has no data-pattern, or just an all-dark pattern220 x. Accordingly, the memory cells in the second portion 240B areassociated with a plurality of empty blocks. They store no content andform a reserved space. Here, a “block” is the smallest allocation unitof a memory that can be addressed by a user (or, a host). A “data block”is a block whose data has been written, while an “empty block” is ablock whose data has not been written. To make it economically feasibleto salvage the original data-mask, the total number of the memory cellsin the first portion 240A is more than the total number of the memorycells in the second portion 240B in this preferred embodiment.

Due to the rules governing memory allocation, slack space cannot beavoided in a mask-ROM. Although both contain empty blocks, slack spacein prior art can be easily distinguished from the reserved space of thepresent invention. Because it is wasteful, prior art purposely minimizesslack space in a mask-ROM, generally to under 1% of the total memoryspace. In contrast, the present invention purposely includes a reservedmask-region associated with the reserved space to accommodate a futurenew content. To further distinguish the present invention from priorart, the reserved space is preferably more than 10% of the total memoryspace. Namely, the reserved mask-region preferably occupies at least 10%of the original data-mask. Because memory cells are uniformlydistributed in a mask-region, this implies that the total number of thememory cells in the second portion 240B is roughly more than ˜10% of thetotal number of the memory cells in the first portion 240A.

FIG. 3BA is the cross-sectional view of the updated mask-ROM_(RS) array30* along the cut-line BB′ of FIG. 3BB; FIG. 3BB is the top view of theupdated data-pattern 250* of the data-layer 220 and its relativeplacement with respect to the address lines 210 a . . . ; 230 a . . . .Here, the original data-patterns 220 a-220 c remain the same. However,updated data-patterns 220 d, 220 e representing the new content arewritten into the region 260B* of the data-layer 220. Accordingly, thememory cells in the second portion 240B* stores the new content.

Referring now to FIGS. 4-5C, a preferred mask-ROM_(RS) 50 and itsaddress-mapping tables are shown. As illustrated in FIG. 4, thepreferred mask-ROM_(RS) 50 includes an interface 52 for physicallyconnecting to and electrically communicating with a variety of hosts.The interface 52 includes contacts 52 x, 52 y, 52 a-52 d which arecoupled to corresponding contacts in a host receptacle. For example, thehost provides a voltage supply V_(DD) and a ground voltage V_(SS) to themask-ROM_(RS) 50 through the power contact 52 x and the ground contact52 y, respectively; the host further exchanges address/data with themask-ROM_(RS) 50 through signal contacts 52 a-52 b. Here, a host is anapparatus that directly uses the mask-ROM_(RS) 50, and the address/dataused by the host are logical address/data.

The preferred mask-ROM_(RS) 50 comprises at least a mask-ROM_(RS) array30 and an address translator 38. The mask-ROM_(RS) array 30 is similarto those disclosed in FIGS. 3AA-3BB. The address translator 38 convertslogical addresses from the host to physical addresses of themask-ROM_(RS) array 30. Here, the logical addresses are represented onan internal bus 58, while the physical addresses are represented on anexternal bus 54 (including signals from contacts 52 a-52 d). The addresstranslator 38 comprises a non-volatile memory (NVM) for storing anaddress mapping table 38, which maintains links between the logicaladdresses and the physical addresses. During read, upon receiving thelogical address for the memory block to be read, the address translator36 looks up the address mapping table and fetches the physical addresscorresponding to the logical address.

The preferred mask-ROM_(RS) 50 could comprise a plurality ofmask-ROM_(RS) arrays. In addition, the mask-ROM_(RS) 30 and the addresstranslator 36 could be formed on separate dies or on a single die. Whenformed on separate dies, the mask-ROM_(RS) array die and the addresstranslator die could be vertically stacked or mounted side-by-side. Theycould form a multi-chip package (MCP) or a multi-chip module (MCM).

FIGS. 5A-5C disclose three exemplary address-mapping tables. Eachaddress-mapping table comprises a plurality of entries. The addresses ofthese entries are logical addresses, while the data stored in theseentries are physical addresses of the content data associated with thelogical addresses. For example, the entry at logical address LA1includes the physical address PA(8 a) of at least one memory blockstoring at least a portion of the content 8 a.

The first address-mapping table 38 in FIG. 5A is for an originalmask-ROM_(RS) 30. Data are written into the original mask-ROM_(RS) 30using the original data-mask 6 of FIG. 2A. The entries at logicaladdresses LA1-LA8 include the physical addresses for the contents 8 a-8e, 8 g-8 i, respectively.

The second address-mapping table 38* in FIG. 5B is for a first preferredupdated mask-ROM_(RS) 30*. Data are written into this updatedmask-ROM_(RS) 30* using the updated data-mask 6* of FIG. 2B. In thisupdated mask-ROM_(RS) 30*, a new content 8 f is added to the originalcontent. Accordingly, a new entry is added to the logical address LA9 ofthe address-mapping table 38*. It contains the physical address PA(8 f)for the content 8 f. To add new entries, the NVM storing theaddress-mapping table 38* is preferably a writable memory, which can beprogrammed at least once. One example of the writable memory is anantifuse-based memory, or a flash memory.

The third address-mapping table 38** in FIG. 5C is for a secondpreferred updated mask-ROM_(RS) 30*. Data are written into this updatedmask-ROM_(RS) 30* using the updated data-mask 6* of FIG. 2B. In thisupdated mask-ROM_(RS) 30*, an upgrade content 8 f is included to replacean outdated content 8 e. Accordingly, the entry PA(8 e) at LA5 isreplaced by the physical address(es) PA(8 f) for the content 8 f. Inother words, the address-mapping table 38** does not contain thephysical address(es) of the outdated content 8 e. To replace entries,the NVM storing the address-mapping table 38** is preferably are-writable memory, which can be programmed many times. One example ofthe re-writable memory is a flash memory.

In the updated mask-ROM_(RS) 30* of FIG. 5C, contents 8 a-8 d, 8 g-8 iare not replaced by any upgrade contents. They are referred to aspermanent contents. To make it economically feasible to salvage theoriginal data-mask, a substantial portion of the original data-maskshould represent the permanent contents. In other words, the memorycells storing the permanent contents should be more than the memorycells storing the outdated content or the upgrade content, as isreflected in FIG. 5C.

While illustrative embodiments have been shown and described, it wouldbe apparent to those skilled in the art that may more modifications thanthat have been mentioned above are possible without departing from theinventive concepts set forth therein. The invention, therefore, is notto be limited except in the spirit of the appended claims.

What is claimed is:
 1. A mask-programmed read-only memory (mask- ROM)family, comprising: a first mask-ROM die comprising at least a firstmemory array; a second mask-ROM die comprising at least a second memoryarray; wherein said first and second memory arrays are same except for areserved portion, said reserved portion comprising a same plurality ofmask-ROM cells in said first and second memory arrays, wherein allmask-ROM cells in the reserved portion of said first memory array have asame structure, and the mask-ROM cells in the reserved portion of saidsecond memory array have at least two structures.
 2. The mask-ROM familyaccording to claim 1, wherein all mask-ROM cells in the reserved portionof said first memory array comprise a data layer.
 3. The mask-ROM familyaccording to claim 1, wherein all mask-ROM cells in the reserved portionof said first memory array comprise no data layer.
 4. The mask-ROMfamily according to claim 1, wherein at least selected mask-ROM cells inthe reserved portion of said second memory array comprise a data layer.5. The mask-ROM family according to claim 1, wherein at least selectedmask-ROM cells in the reserved portion of said second memory arraycomprise no data layer.
 6. The mask-ROM family according to claim 1,wherein the total number of the mask-ROM cells in the reserved portionis more than 10% of the total number of the mask-ROM cells in said firstmemory array.
 7. The mask-ROM family according to claim 1, wherein thetotal number of the mask-ROM cells in the reserved portion is more than10% of the total number of the mask-ROM cells in said second memoryarray.
 8. The mask-ROM family according to claim 1, wherein each of saidfirst and second mask-ROM dice further comprises an address translator.9. The mask-ROM family according to claim 8, wherein said addresstranslator comprises a non-volatile memory for storing anaddress-mapping table.
 10. The mask-ROM family according to claim 9,wherein said non-volatile memory is a re-writable memory.
 11. Themask-ROM family according to claim 10, wherein said re-writable memoryis a flash memory.